Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M1/00—Details of apparatus for conversion
  • H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
  • H02M1/4208—Arrangements for improving power factor of AC input
  • H02M1/4225—Arrangements for improving power factor of AC input using a non-isolated boost converter
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
  • H05B41/14—Circuit arrangements
  • H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
  • H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
  • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Definitions

• the present invention relates to a method for controlling the power factor of a power supply line and to a corresponding control circuit.
• the invention particularly relates, but not exclusively, to a control circuit using a PFC (acronym of the English "Power Factor Corrector") cell for controlling an electronic driving ballast of a fluorescent lamp and the following description is made with reference to this field of application for convenience of illustration only.
• PFC acronym of the English "Power Factor Corrector Corrector
• the PFC cell 10 has a first II and second input terminal 12, as well as a first O l and second output terminal 02.
• the first input terminal II is connected to the first output terminal O l by means of the series of an inductor L and a diode D, connected to each other in correspondence with an inner circuit node X.
• the second input terminal 12 is directly connected to the second output terminal 02.
• the controlled switch SW is inserted between the inner circuit node X and the second input terminal 12, i.e. the second output terminal 02 and it has a driving terminal connected to a convenient driving circuit 12.
• the PFC cell 10 is connected to a first Tl and a second network terminal T2 by means of a diode bridge 11.
• the diode bridge 11 comprises a first pair of diodes D 1 , D2 inserted between the first input terminal II and the second input terminal
• the diode bridge 11 comprising the pairs of diodes
• the PFC cell 10 also has the input II, 12 and output O l, 02 terminals respectively connected to a first CI and a second capacitor C2.
• the PFC cell 10 is finally connected to a load Z inserted between the output terminals Ol and O2.
• the assembly of the capacitor C2 and the PFC cell 10 substantially realises an active filter driven by the driving circuit 12 and being capable of controlling the harmonic content of the power absorbed by the load.
• the switch SW is an electronic switch realised with an active component of the MOSFET type, driven by the integrated IC driving circuit 12 so as to regulate the conduction time thereof.
• the technical problem underlying the present invention is to provide a driving method and a corresponding topology of PFC cell, particularly for electronic ballasts, having a more favourable cost- performance ratio, thus overcoming the limits and drawbacks still affecting prior art PFC cells with integrated IC driving circuit. Disclosure of Invention
• the solution idea underlying the present invention is to exploit the intrinsic electric features of a bipolar power transistor to modulate the transistor conduction time and to use a feedback driving of the control terminal thereof to regulate such a modulation.
• the technical problem is solved by a power factor control method as previously indicated and defined in the characterising part of claim 1.
• the problem is also solved by a power factor control circuit as previously indicated and defined in the characterising part of claim 11.
• Figure 1 schematically shows a PFC cell based on the principle of the IC-driven boost converter
• Figure 2 schematically shows a block diagram of an electronic ballast for fluorescent lamps realised according to the invention
• Figures 3A and 3B show preferred embodiments of details of the block diagram of figure 2
• Figure 4 schematically shows a circuit embodiment of an electronic ballast comprising a control circuit of figure 2
• Figures 5A-5B, 6A-6B, 7A-7B and 8 show the trend in time of signals inside the control circuit of figure 2.
• control circuit 20 is connected to a power supply line by means of a filter input section 11 of the type comprising a diode bridge and it is connected to an electronic ballast 13 being connected in turn to a fluorescent lamp 14.
• the assembly of the input section 11, the control circuit 20, the electronic ballast 13 and the fluorescent lamp 14 is a fluorescent lighting system.
• the control circuit 20 comprises a PFC cell 15 and a regulation block
• the PFC cell 15 is of the self-oscillating type and the electronic ballast 13 and the fluorescent lamp 14 are the load thereof.
• the PFC cell modulates the conduction time by using the storage time of a bipolar transistor, while the regulation block both corrects and protects such a PFC cell.
• the PFC cell 15 of the control circuit 20 according to the invention has a first II and second input terminal 12 connected to respective output terminals of the input section 11 , as well as a first Ol and second output terminal 02 connected to respective input terminals of the electronic ballast 13.
• the PFC cell 15 has a third input terminal 13 connected to the electronic ballast 13 and receiving therefrom a driving signal Sosc, as well as a forth input terminal 14 connected to an output terminal O4 of the regulation block 16 and receiving therefrom a regulation signal Sreg.
• the PFC cell 15 receives an oscillating driving signal Sosc.
• the regulation block 16 has in turn a first input terminal 15 connected to the first output terminal 01 of the PFC cell 15 and receiving an output signal Sout and a second input terminal 16 connected to the first input terminal II of the PFC cell 15 and receiving a primary input signal Sin.
• the regulation block 16 has a third input terminal 17 connected to the electronic ballast 13 and receiving therefrom a pre-heating signal Spreh.
• the PFC cell 15 essentially comprises a conveniently driven bipolar transistor TB 1.
• the PFC cell 15 has the first input terminal II connected to the first output terminal 01 by means of the series of an inductor L and a diode D, connected to each other in correspondence with an inner circuit node X.
• the second input terminal 12 is directly connected to the second output terminal 02.
• the bipolar transistor TBl is inserted between the inner circuit node X and the second input terminal 12, i.e. the second output terminal O2 and it has a control terminal, particularly a base terminal Bl, connected, by means of an RC network 17, to a winding T of a transformer, connected in turn to the second output terminal 02.
• TB 1 is connected to the winding T by means of the series of a first resistor Rl and a capacitor C of the RC network 17, as well as to the second output terminal 02 by means of a second resistor R2 of the RC network 17.
• the interconnection point between the first resistor Rl and the capacitor C of the RC network 17 defines the forth input terminal 14 of the PFC cell 15.
• the interconnection point between the capacitor C of the RC network 17 and a winding T of a transformer, connected in turn to the second output terminal 02 defines the third input terminal 13 of the PFC cell 15.
• the PFC cell 15 according to the invention implements a modulation method of the conduction time of the bipolar transistor TBl exploiting the well known phenomenon according to which the charges injected in the base terminal of a bipolar transistor allow the bipolar transistor saturation effect and they determine the conduction time thereof.
• the PFC cell 15 according to the invention thus succeeds in modulating the transistor turn-on time without introducing any integrated circuit, as it happens instead in prior art circuits.
• the PFC cell 15 is a circuit topology interposing, between the rectifying-bridge input section 11 and a high frequency section such as the electronic ballast 13, a network comprising an inductor, a diode and a bipolar transistor changing the wave-form envelope of the current absorbed by the power supply line, making the envelope thereof almost sinusoidal and thus allowing a power factor with values close to one to be obtained.
• the capacitor C in series with the base terminal Bl of the bipolar transistor TB l, together with the resistance Rl always in series with this base terminal Bl, determine the conduction time constant of the bipolar transistor TBl and they allow a duty cycle being less than 50% to be realised.
• the duty cycle regulation effect is obtained by exploiting the features of the RC network 17 together with the storage time changes of the bipolar transistor TBl in correspondence with the different currents flowing in the collector terminal which must be switched by the bipolar transistor TB 1.
• the bipolar transistor TB 1 since the bipolar transistor TB 1 turns off only when the charges stocked in the base region have been all extracted, a certain delay occurs between the phase wherein the voltage does not bias the base terminal Bl any more and the time wherein the bipolar transistor TB 1 actually turns off.
• the storage time is linked to the values of the current involved and, for the same base current in the conduction phase, it increases as the collector current decreases.
• the transistor regulates the power factor PF through a modulation of the conduction time determined by the storage time thereof.
• the PFC cell 15 of the control circuit 20 is substantially an active PFC cell being capable of modulating the conduction time of the bipolar transistor TBl.
• a PFC cell 15 of the self-oscillating type is used, being driven by a signal Sosc coming from the electronic ballast 13.
• the control circuit 20 also comprises a regulation block 16, connected to the PFC cell 15 and shown in greater detail in figure 3B.
• the regulation block 16 has a first 15 and a second input terminal 16 connected to each other by means of a first R3 and a second resistive element R4, interconnected in correspondence with a first inner circuit node Yl .
• the regulation block 16 essentially comprises a supplementary transistor Q2 of the bipolar type being inserted between an output terminal 04 of the regulation block 16 and a voltage reference, particularly a ground GND, and having a control terminal, particularly a base terminal B2 connected to a second inner circuit node Y2.
• a Shottky diode Ds is inserted between the output terminal 04 and a collector terminal of the supplementary transistor Q2.
• the regulation block 16 also has a third input terminal 17 connected to the second inner circuit node Y2 by means of the series of a diode D5, a resistor R5 and a first Zener diode Dzl .
• a second Zener diode Dz2 is inserted between the first Yl and the second inner circuit node Y2.
• the regulation block 16 comprises an electrolytic capacitor C5 inserted between a third inner circuit node Y3 and the ground GND, this third inner circuit node Y3 being the interconnection point between the diode D5 and the resistor R5.
• the regulation block 16 implements the regulation phase of the obtained conduction time modulation of the bipolar transistor TBl of the PFC cell 15, carrying on a correction thereof for the third harmonic distortion (THD) and a regulation of an output power value by means only of the regulation signal Sreg applied to the forth input terminal 14 of the PFC cell 15.
• the regulation block 16 also ensures a protection of the transistor TBl of the PFC cell 15 during the start-up phase, limiting an input voltage value thereof as soon as a corresponding current value reaches high values.
• the regulation block 16 uses three input signals: the primary input signal Sin corresponding to the line voltage; the output signal Sout corresponding to the output voltage signal of the PFC cell 15; - the pre-heating signal Spreh corresponding to a voltage value being proportional to a start-up current during the preheating and turn-on phases of the fluorescent lamp 14.
• the regulation block 16 serves to reduce the conduction duty-cycle of the bipolar power transistor TBl comprised in the PFC cell 15, if necessary, by limiting the current reaching the base terminal B 1 thereof.
• the regulation block 16 advantageously according to the invention, uses as input signal Sin the rectified sinusoidal line voltage value.
• the regulation block 16 advantageously uses the output signal Sout of the PFC cell 15.
• the regulation block 16 advantageously uses the value of the alternate voltage of the secondary winding T driving the PFC cell 15 as the pre-heating signal Spreh applied to the third input terminal 17. In particular, this voltage is rectified by the diode D5 and clamped by the capacitor C5.
• the present invention provides a power factor control method of a power supply line through the modulation of the conduction time of a bipolar transistor comprised in a PFC cell.
• the control method provides that the modulation of the bipolar transistor conduction time is performed by means of a control signal derived from an elementary alternate- trend signal applied to the base terminal Bl of the bipolar transistor TBl, particularly drawn from a winding of a transformer and applied to the base terminal by means of the RC network 17.
• a control signal is required to drive the base terminal Bl of the bipolar transistor TBl, particularly generated by an integrated circuit serving as a modulator, but this control signal is advantageously drawn from an already existing signal.
• this already existing signal is a signal drawn through a supplementary winding T on a transformer already comprised in applications which generally use transformers operating at high frequency.
• a voltage signal generated on the transformer thus bias the base terminal B 1 of the bipolar transistor TB 1 by means of the RC network 17, essentially comprising a capacitor and two resistors.
• the control method also provides a regulation phase of the conduction time modulation of the bipolar transistor TB 1 by feedback-driving the base terminal Bl thereof.
• this regulation phase provides a current injection in this base terminal Bl being performed by the supplementary transistor Q2 in response to a value of a regulation signal Sreg.
• the conduction action of the supplementary transistor Q2 interacts with the natural modulation due to the storage time change of the bipolar transistor TB 1 as follows: it reduces the charging time constant of the capacitor C, reducing the time of the turn-on base current Ibon of the bipolar transistor TB 1. it realises a path to ground for the turn-on base current Ibon of the bipolar transistor TBl, reducing the amplitude thereof.
• the combination of the two above-mentioned effects allows a reduction of the conduction duty-cycle of the bipolar transistor TBl to be obtained.
• the conduction of the supplementary transistor Q2 helps to correct the third harmonic distortion (THD) and to reduce the power increase occurring when the line voltage value increases.
• TDD third harmonic distortion
• the regulation block 16 also implements a protection phase of the bipolar transistor TBl always through the conduction of the supplementary transistor Q2.
• this protection phase triggers only in the start-up phase of the fluorescent lamp 14 weighting much more on the conduction of the supplementary transistor Q2, considerably reducing the output voltage value of the PFC cell 15.
• An application of the control circuit 20 being provided is schematically shown in figure 4 for a lighting system.
• the driving voltage of the bipolar transistor TBl of the PFC cell 15 is obtained by means of an auxiliary winding T on a transformer of an electronic ballast 13.
• the control circuit 20 is inserted in the power supply of this electronic ballast 13 and connected to a first and a second network terminal Tl, T2 by means of an input section 11 of the diode bridge type.
• the control circuit 20 is also uncoupled at the input and output thereof by means of a first CI and a second capacitor C2.
• the input section 11 in figure 4 also comprises a supplementary diode D6 suitable to realise a filtering block in association with the first capacitor CI .
• the PFC cell 15 comprised in the control circuit 20 has the first and second input terminals 11 , 12 connected to the input section 11 and the first and second output terminals 01 , 02 connected to the electronic ballast 13.
• first and second input terminals II, 12 are connected to each other by means of the first capacitor CI and these first and second output terminals Ol, O2 are connected to each other by means of the second capacitor C2.
• Figures 5A-5B, 6A-6B, 7A-7B and 8 show the wave-forms related to the collector-emitter voltage Vce, the collector current Ic and the base current lb of the bipolar transistor TBl, as well as the network current In, respectively comprising and not comprising a regulation block 16 realised according to the invention.
• Figures 5A and 5B show the trend of a network current signal In, a collector current value Ic of the bipolar transistor TBl and a voltage value between the collector and emitter terminals Vce again of the bipolar transistor TB 1. It can be immediately noticed that the trend of the network current In in figure 5B is almost sinusoidal unlike the wave-form of this network current In shown in figure 5B, without the regulation block 16. The substantially sinusoidal trend of the network current In induced by the regulation block 16 results in a lower third harmonic distortion (THD). In particular, from experimental tests carried out by the Applicant itself, the following results have been obtained: Table I - control circuit 20 with regulation block 16 according to the invention
• figure 6B shows a modulation of the base current lb which cannot be found in figure 6A.
• this modulation operates on the collector current Ic to obtain low values of the third harmonic distortion (THD) on the current absorbed by the network.
• figures 7A and 7B show two details (indicated with Tl and T2 in figure 6B) corresponding to low and high values respectively of the collector current Ic.
• the turn-on time of the bipolar transistor TB l is determined by the charge injection phase in the base terminal Bl thereof and by the charge extraction.
• figure 8 shows the detail related to the pre-heating and start-up phases of the fluorescent lamp 14 with corresponding intervention of the protection realised by the regulation block 16 of the control circuit 20.
• control circuit according to the invention can be used in all those cases when it is necessary to modulate the conduction time of a power device without resorting to systems using integrated circuits and thus not exclusively electronic ballasts, used by way of non-limiting example.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Rectifiers (AREA)
• Control Of Electrical Variables (AREA)
• Direct Current Feeding And Distribution (AREA)

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• 2004
  • 2004-05-18 EP EP04745148A patent/EP1761832B1/de not_active Expired - Fee Related
  • 2004-05-18 BR BRPI0418843-8A patent/BRPI0418843A/pt not_active Application Discontinuation
  • 2004-05-18 WO PCT/IT2004/000280 patent/WO2005111758A1/en active Application Filing
  • 2004-05-18 CN CNB2004800430682A patent/CN100511081C/zh not_active Expired - Fee Related
  • 2004-05-18 DE DE602004017910T patent/DE602004017910D1/de not_active Expired - Fee Related
  • 2004-05-18 MX MXPA06013393A patent/MXPA06013393A/es not_active Application Discontinuation
• 2006
  • 2006-11-17 US US11/601,460 patent/US7852014B2/en not_active Expired - Fee Related

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